Practical Strategies For Condensing Boiler Retrofits

As buildings age, so do the major central equipment within the building, making it a prime opportunity for a boiler system retrofit. Older systems typically are made up of non-condensing boilers that operate in the 200ºF to 180°F range with 160ºF to 140°F returns. As boiler designs have advanced to include condensing technology, it is important to understand how to implement condensing boilers into a system to maximize operating efficiencies.

There are many types of hydronic boilers available today, both non-condensing and condensing. Non-condensing boilers are designed to operate with design return water temperatures above 140°F to prevent condensing of the moisture in the flue gases. This is because they are constructed of materials such as carbon steel, cast iron or copper, which are unable to withstand the corrosive condensate produced with condensing.

Non-condensing boilers generally operate with efficiencies less than 87%, with many well below this level. They can also have system piping limitations, both to maintain the minimum return water temperature as well as delta T or minimum flow requirements.

While condensing boilers are more efficient than non-condensing boilers, the latter generally have higher temperature limits, often with higher design-pressure capabilities. In addition, non-condensing boilers are available in larger capacities and often include the capability for a variety of back-up fuels, and their initial equipment cost is often less.